The present invention relates to the use of A3 subtype adenosine receptor antagonists, calmodulin antagonists and antiestrogens for reduction of intraocular pressure.
The aqueous humor of the eye is formed by the ciliary epithelium, which comprises two cell layers: the outer pigmented epithelial (PE) cells facing the stroma and the inner nonpigmented epithelial (NPE) cells in contact with the aqueous humor. Secretion is generally thought to reflect a primary transfer of solute, largely NaCl, from the stroma to the aqueous humour, providing an osmotic driving force for the secondary osmotic transfer of water down its chemical gradient (Cole,. Exp. Eye Res. 25 (Suppl.), 161-176, 1977), although a more direct coupling between water and solute may also proceed across epithelia (Meinild et al. J. Physiol. 508: 15-21, 1998). One major factor governing the rate of secretion is the rate of chloride ion (Clxe2x88x92) release from the NPE cells into the aqueous humor (Civan, News Physiol. Sci. 12:158-162, 1997). The activity of Cxe2x88x92 channels is likely to be a rate-limiting factor in aqueous humour secretion, given the low baseline level of channel activity and the predominance of the chloride anion in the fluid transferred (Coca-Prados et al., Am. J. Physiol. 268: C572-C579, 1995). The secretion of aqueous humor into the eye is believed to result as a consequence of two opposing physiological processes: fluid secretion into the eye by the NPE cells and fluid reabsorption (secretion out of the eye) by the PE cells. Thus, both release of Cxe2x88x92 by the nonpigmented ciliary epithelial (NPE) cells into the adjacent aqueous humour would enhance secretion, and Cxe2x88x92 release by the pigmented ciliary epithelial (PE) cells into the neighboring stroma would reduce net secretion (Civan, Current Topics in Membranes 45: 1-24, 1998).
Recently, adenosine has been found to activate NPE Clxe2x88x92 channels which subserve this release (Carre et al., Am. J. Physiol. (Cell Physiol. 42) 273:C1354C-C1361, 1997). Purines, a class of chemical compounds which includes adenosine, ATP and related compounds, may regulate aqueous humour secretion, in part through modifying Clxe2x88x92-channel activity. Both NPE and PE cells have been reported to release ATP to the extracellular surface, where ATP can be metabolized to adenosine by ecto-enzymes (Mitchell et al. Proc. Natl. Acad. Sci U.S.A. 95: 7174-7178, 1998), and both cell types possess adenosine receptors (Wax et al., Exp. Eye Res. 57:89-95, 1993; Wax et al, Invest. Ophthalmol. Vis. Sci., 35:3057-3063, 1994; Kvanta et al., Exp. Eye Res. 65:595-602, 1997) and ATP receptors (Wax et al., supra., 1993; Shahidullah et al., Curr. Eye Res. 16:1006-1016, 1997). Furthermore, in vitro studies of rabbits have associated A2-adenosine receptors with increased secretion and elevated intraocular pressure (Crosson et al., Invest. Ophthalmol. Vis. Sci. 37:1833-1839, 1996) and A1-adenosine receptors with the converse (Crosson, J. Pharmacol. Exp. Ther. 273:320-326, 1995). Qualitatively similar associations with intraocular pressure, but not with secretion, have been observed in cynomologus monkeys (Tain et al., Exp. Eye Res., 64: 979-989, 1997). A particular role for Clxe2x88x92 channels has been suggested by the observations that adenosine agonists stimulate Clxe2x88x92 channels of immortalized human and freshly-dissected bovine NPE cells and of aqueous-oriented Clxe2x88x92 channels of the intact rabbit iris-ciliary body (Carrxc3xa9 et al., supra., 19971. Adenosine triggered isotonic shrinkage of cultured human cells from the HCE cell line. The contribution of Clxe2x88x92 channels to this shrinkage was identified by performing the experiments in the presence of the cation ionophore gramicidin. In addition, adenosine produced a Clxe2x88x92 dependent increase in short-circuit current across rabbit iris-ciliary body while the non-metabolizable adenosine analogue 2-Cl-adenosine was shown to activate Clxe2x88x92 currents in HCE cells using the whole cell patch-clamp technique. Although this study clearly established that adenosine could activate Clxe2x88x92 channels on NPE cells, the concentrations of agonist used were capable of stimulating all four known adenosine receptor sub-types: A1, A2A, A2B and A3 (Fredholm et al., Pharmacol Rev., 46:143-156, 1994; Fredholm et al., Trends Pharmacol, Sci., 18:79-82, 1997; Klotz et al., Naunyn Schmiedebergs Arch. Pharmacol., 357:1-9., 1998). Ciliary epithelial cells are known to possess A1 A2A and A2B adenosine receptors (Kohno et al., Blood, 88:3569-3574, 1996, Stambaugh et al., Am. J. Physiol. 273 (Heart Circ. Physiol. 42):H501-H505, 1997; Wax et al., supra., 1994). Although stimulation of these receptors can be associated with specific changes in the levels of second messengers cAMP (Crosson, supra.; Stambaugh et al., supra.; Wax et al., supra., 1994) and Ca2+ (Farahbakhsh et al., Exp. Eye Res., 64:173-179, 1997), the effect of these receptors upon Clxe2x88x92 channels of NPE cells was unknown.
Alternatively, the intraocular pressure could be reduced by stimulating reabsorption of aqueous humor. In principle, this could be achieved by activating chloride channels on the basolateral surface of the pigmented cell layer. This would release chloride back into the stroma. One way to accomplish this with the PE cells has been identified using the antiestrogen tamoxifen. Tamoxifen is known to exert multiple actions on biological cells. However, recently, Mitchell et al. (Invest Ophthalmol. Vis. Sci. 38(Suppl.):S1042, 1997) have noted that the only known action of tamoxifen which could account for the phenomenon is its antiestrogenic activity, probably on the plasma membrane.
Glaucoma is a disorder characterized by increased intraocular pressure that may cause impaired vision, ranging from slight loss to absolute blindness. The increased intraocular pressure is related to an imbalance between production and outflow of the aqueous humor. Current drugs prescribed for glaucoma, in the form of eyedrops, include pilocarpine, timolol, betaxolol, levobunolol, metipranolol, epinephrine, dipivefrin, latanoprost, carbachol, and potent cholinesterase inhibitors such as echothiophate and carbonic anhydrase inhibitors such as dorzolamidet. Many of these effective approaches to medical therapy of glaucoma involve a reduction in the rate of flow into the eye. However, none of these drugs are satisfactory, in part due to side effects.
Because of side effects of available agents and inconvenient dosing schedule, there is an ongoing need for compounds capable of reducing intraocular pressure for the treatment of glaucoma with improved efficacy, prolonged action and reduced side effects. The present invention addresses this need.
One embodiment of the present invention is a method for reducing intraocular pressure in an individual, comprising the step of administering to the individual an effective intraocular pressure-reducing amount of a pharmaceutical composition comprising an A3 subtype adenosine receptor antagonist. In one aspect of this preferred embodiment, the A3 receptor antagonist is a dihydropyridine, pyridine, pyridinium salt or triazoloquinazoline. Preferably, the A3 subtype receptor antagonist is selected from the group consisting of MRS-1097, MRS-1191, MRS-1220 and MRS-1523. Advantageously, the pharmaceutical composition is administered topically, systemically or orally. Preferably, the pharmaceutical composition is an ointment, gel or eye drops.
Another embodiment of the present invention is a method for reducing intraocular pressure in an individual, comprising the stop of administering to the individual an effective intraocular pressure-reducing amount of a pharmaceutical composition comprising an antiestrogen. Preferably, the antiestrogen is tamoxifen. Advantageously, the pharmaceutical composition is administered topically, systemically or orally. Preferably, the pharmaceutical composition is ointment, gel or eye drops.
The present invention also provides a method for reducing intraocular pressure in an individual, comprising the step of administering to the individual an effective intraocular pressure-reducing amount of a pharmaceutical composition comprising a calmodulin antagonist. Preferably, the calmodulin antagonist is trifluoperazine. Advantageously, the pharmaceutical composition is administered topically, systemically or orally. Preferably, the pharmaceutical composition is ointment, gel or eye drops.
Another embodiment of the present invention is an A3 subtype adenosine receptor antagonist for use in reduction of intraocular pressure. Preferably, the A3 subtype adenosine receptor antagonist is MRS-1097, MRS-1191 or MRS-1523.
The present invention also provides the use of an antiestrogen in the preparation of a medicament for the reduction of intraocular pressure. Preferably, the antiestrogen is tamoxifen.
The present invention also provides a calmodulin antagonist for use in reduction of intraocular pressure. Preferably, the calmodulin antagonist is trifluoperazine.